Solid propellant is used in various types of rocket and missile motors, and is typically composed of a polymer, such as polybutadine, cellulose acetate, or polyvinylchloride, and a finely ground oxidizer, such as a perchlorate or nitrate salt. Various types of modifiers, such as plasticizers, burn-rate catalysts, or stabilizing agents, can be added to the propellant mixture to modify the structural or performance characteristics. In the manufacture of solid propellants, the polymer, which acts as the fuel, is typically mixed with the oxidizer(s) and modifier(s) in an uncured, fluid state. A curing or cross-linking agent is then added to the mixture before it is cast in the desired shape and cured.
Conventional planetary mixers and paint shaker-type equipment are often used to mix solid propellants. Planetary and double planetary mixers, such as those provided by Baker Perkins Inc., of 3223 Kraft Ave. S.E., Grand Rapids, Mich. 49512, and Charles Ross & Son Company, of 710 Old Willets Path, Hauppauge, N.Y. 11788, typically include two curved blades that extend into the propellant mix vessel and rotate about their own axes, while orbiting the mix vessel on a common axis. The blades continually advance around the periphery of the mix vessel during the mixing process, while the mix vessel remains stationary. Paint shaker-type mixers, such as those provided by Red Devil Equipment Co., of 14900 21st Ave. N., Plymouth, Minn. 55447, shake the mix vessel back and forth at a high frequency to fully mix the propellant ingredients together.
The ratio of polymer to oxidizer in solid propellant formulations is generally such that the resultant combustion products are low molecular weight gaseous products, such as carbon monoxide, nitrogen, hydrogen, water, and hydrogen chloride. To modify the linear burn rate of propellant, the oxidizer is typically ground to a specific particle size, such as about 100 to 300 microns. Finer particle distributions generally produce higher burn rates and, consequently, greater thrust. Using an oxidizer that is ground too fine, however, can result in propellant formulations that are very viscous and difficult to mix using the current state-of-the-art processes. As a result, conventional propellant formulations are generally constrained to linear burn rates ranging from about 0.1 inch per second to about 1.5 inches per second at chamber pressures of about 1,000 psi. Another shortcoming of conventional mixing processes is the amount of time it typically takes to achieve a relatively homogenous propellant mixture. Conventional planetary mixers, for example, typically require about 6 to 8 hours to provide a relatively homogenous mixture, while conventional paint shaker-type equipment can require from 1 to 2 hours.
Accordingly, it would be advantageous to have a method of producing relatively homogenous propellant mixtures in a relatively short period of time. In addition, it would also be advantageous to have a method of producing relatively homogenous propellant mixtures having oxidizer particles that are small or fine enough to provide linear burn rates higher than 1.5 inches per second.